Driving Line Auto Repair Blog

Helping you make informed auto repair decisions.

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Are You Normal or Severe?

Ken Gamble Addresses the Age-Old question – How Often Does the Oil Need To Be Changed?

What are Change Intervals?

Oil Change “Intervals” have to do with the time and/or mileage elapsed between recommended changes. There is no disputing that oil needs to be changed. But with improved technology, does the old mantra of “every 3,000 miles” still apply?

Most of us already know that regularly scheduled oil and filter changes are a vital part of routine car maintenance and are necessary for engine longevity.

During the miles between changes, the oil in your vehicle's engine gradually becomes contaminated with soot, metal particles, gasoline and other impurities. As mileage accumulates, so do the contaminants in the oil. Eventually, enough impurities accumulate that the filter cannot remove them and the oil cannot keep them in suspension. When this happens engines collect sludge inside clogging up internal oil passages, which is why its life expectancy is drastically reduced.

Even though modern technology has vastly improved engines and the oils that lubricate them, regularly scheduled oil and filter changes are still a vital part of regular, preventative auto maintenance. The question is: Just how often does the oil need to be changed?

At regular intervals

The old “fatherly advice“ of responsible motorists said, "Change your oil every 3,000 miles!" Today car manufacturers' recommendations for oil changes range from 5,000 to 7,500, or even 10,000 miles for many cars when operated under "normal" driving conditions—more often if conditions are "severe."

Before you relax let me point out that automotive experts list the way most of us drive as “severe”. According to the owner's manuals of many new cars and trucks, normal operation of a vehicle is at least 20 minutes, at a medium speed with a steady throttle, and in a clean environment.

According to one carmaker's owner's manual, the oil change interval is seven months or 7,500 miles under “normal” driving conditions, three months or 3,000 miles under “severe” conditions. This is how “severe” is defined in the manual:

Repeated, short distance driving.

Extended periods of idling or low-speed operation.

Extensive use of brakes.

More than 50 percent driving in heavy city traffic during hot weather above 90 degrees F.

Driving for a prolonged period of time in cold temperatures and/or extremely humid climates.

Driving in dusty conditions or sandy areas.

Driving in areas where salt or other corrosive materials are being used.

Driving on rough or muddy roads.

Driving in mountainous areas.

Well, it looks like your daddy’s advice about oil changes isn't out of date after all. But what about synthetic oils, don't they extend oil change intervals?

A number of car manufacturers do recommend synthetic oil for their high-performance models because of the superior protection from friction and extreme temperatures. The protection comes from the processing required to manufacture the base stock and the different additive packages they require.

Despite this better performance, synthetic additives wear out just as they do in conventional motor oils, and need to be changed. The key is driving conditions — “normal” or “severe”?

How about just changing the oil filter, can a car be driven further in between oil changes? Changing the filter is great, but the oil must be changed along with it, given that the oil's additives wear out and contaminants get into the oil itself. The filter can only capture the bigger particles suspended in the oil, not replenish spent additives.

Pinching Pennies

From an economic point of view, it would appear that waiting for an extra few thousand miles between changes will save money. For example, based on $25 oil changes every 5,000 miles instead of 3,000 miles, more than $300 is saved per 100,000 miles. Sounds pretty good, but if you drive the average of 17,000 miles a year, it will take you almost six years to reach that mileage — or $50 per year savings.

Extending the oil change interval beyond what the manufacturer recommends can seriously shorten the useful life of your engine, and cost you many times the $300 savings. Just ask a professional service technician how often he or she changes the oil and filter on their personal vehicle. Chances are the answer will be 3,000 miles.

Bottom line: Don't push the limits of motor oil and flirt with damaging your car's engine. If you’ll take the initiative in keeping your car performing its best, it will remain reliable and need fewer repairs as time goes by. Don’t run out of car before you run out of payments, ouch!